Electric machines can be used to provide torque for various types of systems, such as, but not limited to, electric drive systems for electrified vehicles in which machine-generated torque is used for vehicle propulsion. Electric drive systems often rely on field-oriented techniques to control machine operation and torque output. Field-oriented control requires feedback current to be provided to a machine controller so that a determination can be made as to whether torque output needs to be adjusted, and any required adjustment can be performed. Accordingly, several current sensors are disposed to detect current and provide the necessary feedback. In a typical arrangement, two current sensors are used specifically for torque control, and a third current sensor is used to detect unintentional torque delivery. A diagnostic algorithm can be designed to sum the readings of all three sensors and compare the sum to a predetermined threshold to detect a torque delivery fault. While the checksum algorithm is designed to detect an error in torque control that leads to an unintentional torque delivery, in many cases it is relied on as a means for detecting a current sensor fault, since most, if not all, field-oriented control systems lack a dedicated fault diagnostic for a current sensor.
However, several problematic issues are associated with the use of a checksum method for sensor fault detection. For instance, there is no consistent approach for determining a threshold for the checksum comparison. Several factors can affect threshold determination, including sensor accuracy, signal noise level and the sensor current range, so a threshold can be sensor and application specific, and its determination can necessitate a time-consuming calibration process. In addition, the inclusion of a third sensor for enabling execution of a checksum algorithm increases the number of system components. When the vehicle drive system includes both a traction motor and a generator, two additional components are added, with each additional component increasing system cost while decreasing overall system reliability.